Generally, as shown in FIG. 8, an injection molding machine for a resin or a metal has the following configuration. That is, a single piston which discharges lubricant by back-and-forth movement caused by compression and decompression of lubricant and a known single continuous flow valve V provided with one discharge port corresponding to this piston and discharge about 0.03 ml to 1.5 ml per shot are used, and these continuous flow valves V are provided at corresponding plural locations through a lubrication pipeline W, and lubricant is supplied from a lubricant pump device Sa to this lubrication pipeline W.
Since it discharges lubricant when actuated by compression and decompression of lubricant, the single continuous flow valve V is required to be decompressed. Accordingly, a lubricant pump Sa which can conduct decompression is used.
Conventionally, as the lubricant pump of this type, a device which supplies lubricant made of grease disclosed in Patent Document 1 (JP-A-H06-137489) or Patent Document 2 (JP-B-H07-81676) is known.
This lubricant pump Sa is, as shown in FIG. 8, a plunger-type pump main body 100 provided with a cylinder and a piston and an electric motor 101 as the actuator which allows the piston to move back and forth and can rotate clockwise and counterclockwise.
This pump main body 100 is driven when the electric motor 101 rotates clockwise, and suctions lubricant stored in a tank 102 and discharges it from a discharge port 104 through a discharge path 103. Between the tank 102 and the discharge path 103, a decompression path 105 is formed. In this decompression path 105, a decompression valve 106 which is driven by the electric motor 101 is interposed. The decompression valve 106 is closed when the electric motor 101 rotates clockwise, and opens when the electric motor 101 rotates counterclockwise. When the discharge port 104 is connected with the lubrication pipeline W, and at the time when lubricant is supplied to this lubrication pipeline W, the electric motor 101 is allowed to rotate clockwise to allow the piston of the pump main body 100 to move back and forth to compress the discharge port 104. On the other hand, at the time when lubricant to the lubrication pipeline W is not supplied, based on signals from a pressure switch 107 or the like, the electric motor 101 is allowed to rotate counterclockwise to open a decompression valve 106, whereby the discharge port is decompressed. In FIG. 8, numeral 108 is a relief valve.